As shown in U.S. Pat. No. 4,677,049, Griffing et al., assigned to the same assignee as the present invention and incorporated herein by reference, diarylnitrones are used as photobleachable compounds to make near-UV (350-450 nm) contrast enhancement lithographic compositions. In copending application Ser. No. 889,573, mid-UV imaging areas (300-350 nm), have been satisfied with certain .alpha.-aryl-N-alkyl nitrones. Recently, efforts have been made to apply contrast enhancement capability to photoresists in the deep-UV regions of 200-300 nm.
At the present time, the only known nitrones which absorb in the 200-300 nm region are dialkylnitrones. However, most dialkylnitrones either quickly hydrolyze and/or dimerize. It would be desirable, therefore, to find organonitrones useful in the deep-UV region which are stable in solution.
The present invention is based on my discovery that certain .alpha.-alkyl-N-alkyl nitrones having the formula, ##STR1## can be used as photobleachable dyes to provide deep UV contrast enhancement layers (CEL) in photolithographic applications, where R is selected from hydrogen and a C.sub.(1-8) alkyl radical, X is a monovalent radical selected from hydrogen and an electron withdrawing radical selected from the class consisting of carbalkoxy, acyl and oxirane, Y is a monovalent aliphatic group selected from R.sup.1, and ##STR2## R.sup.1 is a C.sub.(1-8) alkyl radical, R.sup.2 and R.sup.3 are monovalent radicals selected from hydrogen and C.sub.(1-8) alkyl, Z is a member selected from hydrogen, C.sub.(1-8) alkyl radical or an electron withdrawing radical selected from the class consisting of nitrile, carbalkoxy, and acyl, and R and/or Y can be a C.sub.(3-5) divalent alkylene radical, or a C.sub.(3-5) divalent alkylene radical substituted with one to three monovalent radicals, or a mixture thereof selected from the class consisting of cyano, halogen, carbalkoxy, nitro, amino, and alkylamino, which divalent radicals together can form a C.sub.(5-7) heterocyclic ring.